1. Field of the Invention
The present disclosure relates to a light emitting diode, and more particularly, to a light emitting diode capable of achieving an enhancement in luminous efficacy and a method for fabricating the same.
2. Discussion of the Related Art
Generally, a light emitting diode (LED) is a device, which emits light when current is applied thereto. Such an LED converts electricity into light, using the characteristics of a compound semiconductor. The LED is known to exhibit excellent energy saving effects through high luminosity at low voltage. Recently, brightness problems involved in LEDs have been greatly reduced. As a result, LEDs are being applied to various appliances such as backlight units of liquid crystal display devices, advertising display panels, indicators, home electronic appliances, etc.
In particular, GaN-based LEDs are highlighted as a next-generation light source in that they may be used for various purposes because they generate infrared light or wide light emitting spectrums including infrared light, and they do not include environmentally-harmful substances such as arsenic (As) and mercury (Hg).
FIG. 1A is a perspective view illustrating a general LED. FIG. 1B is a cross-sectional view taken along a line A-A′ in FIG. 1A. FIG. 2 is a sectional view illustrating total reflection occurring within a general LED.
As shown in FIGS. 1A and 1B, the general LED includes a substrate 100, a buffer layer 110 formed over the substrate 100, a first semiconductor layer 130 formed over the buffer layer 110, an active layer 140 formed on a portion of the first semiconductor layer 130, and a second semiconductor layer 150 formed over the active layer 140. The LED also includes an ohmic contact layer 160 formed on the second semiconductor layer 150, using a transparent conductive material, a first electrode pad 180 formed at another portion of the first semiconductor layer 130 where the active layer 140 is not formed, and a second electrode pad 170 formed on the ohmic contact layer 160.
When a part of light generated from the active layer 140 is incident upon another layer having a certain index of refraction at an angle of incidence not less than a critical angle, in the above-mentioned general LED, the incident light is totally reflected in the layer, such that it is confined within the device.
For example, when light is incident upon the substrate 100 at an incidence angle not less than a critical angle, it is totally reflected in the substrate 100, so that it may not pass through boundary surfaces of the substrate 100. As a result, the light may be confined within the device. The light confined within the device vanishes after being repeatedly reflected between layers. Consequently, a reduction in luminous efficacy occurs.